WALTHAM — The goal Friday at TD Garden is to simply win Game 3, to inject a hint of doubt and insecurity into the minds of the New York Knicks, who have played two rather average games yet walked away with resounding victories.

While Celtics coach Doc Rivers has lauded the composition of his team, even after the season-ending injury to Rajon Rondo, eventually he understood that it was flawed, and the cracks from lacking a floor leader are evident. Using Paul Pierce as a point forward not only leads him into more unforced errors because he is playing out of position, it hinders his ability to defend and post up when he is trying to start the offense.

Rondo’s value has increased exponentially over the past few weeks, as the Celtics have realized through trial and error that Avery Bradley is not a true point guard; that issue should be put to rest for coming seasons. The impressive contributions from New York’s Raymond Felton in this series only emphasize the Celtics’ weakness at point guard and how Rondo’s absence has forced several players to adjust their roles.

After the ball-dominating Rondo went down, Jason Terry said he relished the Celtics’ new ball-moving offense, but in all honesty, Terry is better when he is getting passes off screens, when Rondo offers the ball in his sweet spot, as does Courtney Lee.

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As controversial a figure as he may be in the Boston sports market — with some wanting to erect a statue of him in front of TD Garden and others wanting to exile him to the same island as Alfredo Aceves, Josh Beckett, and Albert Haynesworth — Rondo is immensely valuable to the Celtics’ offensive effort.

“There’s no question that the biggest difference in this team is not having Rondo,” said ESPN analyst Tim Legler. “I thought it was actually silly, some of the chatter out there after a six-game winning streak when he went down, ‘Oh, are they better without him?’

“I just thought it was absolutely absurd. I’m a big Rondo guy. I knew there might be some issues at times with him, maybe in the locker room or certain things that he does that people look at negatively.

“The bottom line is this: When you get deep into the season and the games mean a lot more, you’re playing one team over and over that can lock in on your sets, that really makes it difficult to execute your offense because they know what’s coming.

“You need that guy that can improvise and can break off a play and go create offense. That’s what Rondo does, just about better than anybody in this league. You can’t replace that with the guards that they have, you just can’t.”

Rivers, an effective point guard in his day, knows the importance of Rondo and also understands that Bradley, at age 22, is a wild card. He can’t be expected to do anything besides defending particularly well because defense takes up so much energy. The Knicks are daring him to shoot and penetrate.

Felton is capitalizing on Bradley’s defensive aggression by getting past him and into the paint the way a wily veteran should. The education of Avery Bradley is happening as we speak. His responsibility is monumental because the Celtics refused to acquire a true quality point guard following Rondo’s injury.

The idea of Terry or Lee helping out at point guard was an illusion.

“We’re not organized on the halfcourt offensively the way we should be,” Rivers said Thursday. “You’re going to have to play some halfcourt in the playoffs. We just haven’t handled it very well.

“We’ve prepared for it since Rondo went down, we just haven’t handled the pressure well. We can. I know we can. And we will. Right now, we’re a first-option team and then we stand around and watch.”

The acknowledgment that Bradley is not the answer at point guard is no indictment of Bradley’s talent or prowess, but it does allow the organization to plan accordingly.

“It’s a hard role for Avery,” said Rivers. “We’re asking Avery to pressure, pressure, pressure and then try to be something that he’s not. Avery is a good basketball player but we never wanted him to be in the position of facilitating the offense.

“We’re asking a lot. We understand that.”

The Chicago Bulls, knowing that their franchise point guard would miss most, if not all, of the season, went out and picked up Kirk Hinrich, Nate Robinson, and Marquis Teague. They may be a shell of the team they were last season, but they are still formidable.

Trying to navigate through the second half of the season and the playoffs without a natural ballhandler and floor leader was a mistake that may cost the Celtics the season.

They will be back to normal next year when Rondo returns and perhaps they will finally add a natural backup point guard.

But until then, it’s on Bradley, and he has the ability, fortitude, and toughness to be better than he has shown in the first two games.